Synthesis and electrochemical properties of Co-free P2/O3 biphasic Na1-xLixNi0.33Mn0.67O2 cathode material for sodium-ion batteries

Co-free cathode material is an ideal material for developing low-cost sodium ion batteries. Both O3 and P2 single-phases suffer structural degradation, resulting in irreversible structural collapse and rapid capacity decline. Compared with the single-phase crystal structure type O or P, the composite phase crystal structure has attracted the attention of researchers due to its superior performance advantages. Referring to the element composition and crystal structure of Li-rich cathode material, the novel biphasic P2/O3-Na1-xLixNi0.33Mn0.67O2 cathode material was synthesized by solid state method. The introduction of Li+ makes more Na+ in the material remain in the triangular prism position at high charging voltage, which will not destroy the biphasic structure and improve the stability of high rate during the cycle. At 0.1C and 20C rates, Li0.2Na0.8Ni0.33Mn0.67O2 released 132.5 and 70.1 mAh g(-1) discharge specific capacities, respectively. In the deep charging and discharging status, the superior capacity retention of 80.1 % is measured even after 120 cycles of sodium ion extraction and insertion.